At the time of drying such a material as stated above, in order to avoid thermal denaturation thereof, lowering of the evaporating temperature of the moisture contained in the material is contemplated and the vacuum drying method is generally employed for this purpose.
This method is usually performed by moving a belt in a vacuum drying chamber and distributing a material on this belt.
In this case, as a point on which special stress should be laid, there is cited the state of distribution of the material on the belt. In other words, the material should be continuously supplied onto the belt in regular quantities and in a uniform thickness. Should the material fail to be supplied in this state, balance between the quantity of material supplied and the quantity of heat supplied will be lost, resulting in partial occurrence of scorched powder or crude powder due to superheating or insufficient heating to thereby bring about an unsatisfactory product lacking in uniformity of quality.
Accordingly, in order to continuously obtain a product of good quality by easy operation, provision of a feed device capable of distributing a material onto a belt in a quantity opposite to a fixed temperature for heating as well as in a uniform thickness is hoped for.
To cite an instance of this kind of feed device, such a feed pipe as denoted by reference numeral 1 in FIG. 1 has hitherto been used. This feed pipe 1 is of a construction that a plurality of nozzles 3 with a fixed diameter are provided in the lower part of a cylinder 2 at a regular pitch l along the axial direction thereof, and a material fed through an inlet for material 4 disposed on one end of the cylinder is to be distributed onto a belt through said nozzles 3.
However, this feed pipe 1 has been defective in that the internal resistance of the parts extending from the inlet pipe for material 4 to the opposite end varies and accordingly the linear velocity v of the material in a nozzle close to the inlet pipe 4 comes to be the highest and decreases with the advance of the material toward the inner part while the linear velocity v' of the material in a nozzle at the opposite end comes to be the lowest, thereby causing the quantity of the material distributed onto the belt to be uneven.